Statement of the Technical Field
The inventive arrangements relate to energy efficiency improvements in portable radio equipment and more particularly to improvements in transmitter power efficiency in portable radio equipment.
Description of the Related Art
Conventional portable radio transceivers rely on one or more batteries as a primary source of electric power for operating such equipment. A key design specification for a portable radio transceiver is the length of time that the equipment can operate without requiring the batteries to be replaced or recharged. Accordingly, power consumption by such portable radio equipment is an important factor and must be carefully managed.
During transmit operation a transmitter portion of a portable radio transceiver will usually consume significantly more power than a receiver portion of the transceiver. Actual power consumption will depend on the amount of time spent transmitting and the transmitter power consumption characteristics. The transmitter power consumption characteristics can depend on a variety of factors such as the amplifier technology utilized in a particular implementation. But it is not uncommon for the transmitter to be a primary factor in determining battery longevity in a portable radio transceiver system. Within the transmitter, the greatest source of power consumption usually can be found in the final amplifier stage which increases low level radio frequency (RF) exciter signals to much higher power levels.
A high power RF output of a radio transceiver is coupled to an antenna to facilitate wireless transmission. Maximum power transfer from the final output stage of the transmitter to the antenna occurs when the output impedance of the transmitter is matched to the input impedance of the antenna. But antenna input impedance often varies with frequency and with the particular antenna installation. Accordingly, an exact impedance match to the fixed output impedance of the transmitter is often difficult to maintain. This can result in a relatively high voltage standing wave ratio (VSWR) along the transmission line between the transmitter and the antenna. To address this issue, antenna matching networks are commonly used at the RF interface between the transmitter output and the antenna input. The antenna matching network is adjusted so that the antenna appears to have an impedance which approximately matches the output impedance of the transmitter. The correct impedance adjustment or match at the antenna matching network is commonly determined by measuring the VSWR at the output of the transmitter. An optimal match is commonly understood to be attained when the measured VSWR is approximately to 1:1.
Various methods are used to determine a proper adjustment of an antenna matching network. For example, a sensing mechanism such as a directional coupler can be used to detect the VSWR at an antenna port. The directional coupler can detect forward and reflected signals on a transmission line associated with an antenna feed. The signal from the directional coupler is then interpreted by an electronic circuit to adjust a tuning loop. Other systems detect RF load currents of a power amplifier driver circuit (or the power amplifier itself) for purposes of facilitating antenna tuning functions. An exemplary system utilizing such an approach is described in U.S. Pat. No. 8,131,232. Amplifier load currents can indicate how efficient the coupling is to the next stage or antenna. Higher amplitude drive currents and larger phase differences between the current and voltage correspond to a greater impedance mismatch. Accordingly, the current amplitude and/or phase information from such systems can be used as a basis to determine a variation with respect to a reference matching condition.